The present invention relates generally, as indicated, to automatic analyzing systems and, more particularly, to automatic analyzing systems for electroplating baths. Moreover, the invention relates to a method for automatic analysis, particularly of electroplating baths, and to a method and apparatus for automatic analysis and control of baths, such as electroplating baths.
In an electroplating bath or process changes ordinarily occur, for example, in the chemical balance of the bath, as electrochemical reactions occur. To help maintain the quality of the electroplated product and the efficiency of an electroplating bath, it is necessary to analyze the bath for one or more parameters. Shut down of a process or correction of the chemical composition of the bath may be based on the information obtained by such analysis.
One prior analysis technique for electroplating baths employed a Waters Associates Liquid Chromatograph into which a small quantity of liquid specimen manually taken from a bath on a daily basis was manually injected. For accuracy, though, it is desirable that the time lag between drawing a specimen and analysis thereof be minimized; however, using the manual specimen drawing and injecting technique, it is difficult both to minimize that time lag and to hold the same constant for each analysis. Moreover, the manual drawing and injecting of specimens is time consuming and expensive, especially when multiple baths must be separately analyzed on a daily basis. Although carousel-type specimen holders and delivering equipment have been available to provide multiple specimens sequentially to optical analyzing equipment, such as the mentioned liquid chromatograph, the individual specimens still must be manually drawn from respective baths and placed in the carousel which is then operated to provide semi-automatic delivery to the analyzing machine. Another disadvantage with the prior analyzing technique is the limited ability of the analyzing machine; for example, certain components of an electroplating bath may not affect the ultraviolet light of such liquid chromatograph and, thus, may defy detection or analysis thereby.
Historically the analysis of electroplating solutions has met with difficulty. Combinations of traditional chemical analysis, e.g. Peter Wolfram Wild Modern Analysis For Electroplating, (Finishing Publications Limited, Middlesex, U.K., 1974), and qualitative performance analysis, such as the Hull Cell, e.g. U.S. Pat. No. 2,149,344, have had to suffice. One recent innovation has been the use of cyclic stripping voltometry, e.g. U.S. Pat. No. 4,132,605 to characterize quantitatively the performance of a copper electroplating bath. Despite these methods of control and analysis it often occurs that poor plating characteristics manifest themselves over time as the solutions are used. Organic contaminants, trace metals, and oxidation or reduction products from the electrolysis of "brightening" or leveling addition agents may accumulate so as to eventually deleteriously affect performance of the electroplating solution.
In the past the use of chromatographic separation techniques that are reproducible provided proper detection is also employed may show buildup of materials not deliberately added to the electroplating solution. If correlative changes in the concentration of these non-deliberately added compounds with the change in plating performance are noted, the electroplater may be able to anticipate changes in performance before they adversely affect the quality of his work.
To provide frequent analysis, so that meaningful data may be accrued, is a primary intent of this invention.